Hydrophobic materials are used as coatings, as one example only, on microfluidic surfaces encountered on inkjet printheads. Conditions for the manufacture and subsequent operation of an inkjet printhead require that these hydrophobic materials exhibit chemical resistance during processing (exposure to develop solvents, plasma etching and ashing, chemical wet etching), chemical resistance during usage (ink interactions, environmental stability), and mechanical durability (pen manufacturing, printhead servicing). The combination of hydrophobicity, chemical resistance, and mechanical durability are key requirements for any material being evaluated for such purposes.
Preferably, these hydrophobic materials are patterned, so that certain surface regions remain hydrophobic while others are not. This can be accomplished using typical photoresist methodologies where etching the hydrophobic material can be used to remove areas of the material in question. Alternatively, a photopatternable hydrophobic material can be made in which the material can be selectively placed in certain regions using traditional lithography, while also meeting the chemical and mechanical requirements discussed above.
In one such approach, silane surface treatments have been used to create hydrophobic surfaces. While demonstrating characteristics of a hydrophobic surface, the durability of these materials is inadequate for printhead processing and use. If incorporated into a printhead application, servicing the printhead by wiping would remove the hydrophobic layer leaving the printhead surface wettable once again. Thus, silane and other surface treatment approaches are inadequate based on the mechanical durability requirements.
Siloxane materials have also been used as hydrophobic coatings. However, these materials often cannot withstand traditional printhead fabrication processing including, for example, treating the coating material with an oxygen plasma dry etch and/or a wet etchant. Such materials would be considered inadequate based on the chemical resistance requirements.
Accordingly, a need remains for hydrophobic coatings that are photopatternable, can withstand traditional printhead fabrication processing (including without limitation, wet or dry etching, ashing and baking at a high temperature), demonstrate adequate chemical resistance to inks and other environmental factors during use (including oxidation and temperature stress), and/or show adequate mechanical durability so the surface can be mechanically wiped without loss of intended hydrophobic properties.